JP2003028090A - Molecular pump and vacuum pumping device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molecular pump superior in compression performance. SOLUTION: In this molecular pump equipped with a drag pump part having a screw groove 51, a lead shape of the screw groove 51 is formed to be same with a part of a curve expressed in an expression; curve (y)=-b.x<0.5> . At this time, an end part of the partial curve on the coordinate origin side is the turbo molecular pump side of the screw groove 51, and the other end part of the partial curve is the exhaust port side of the screw groove 51. A lead angle ϕof the screw groove 51 becomes smaller as going to the exhaust port side from the turbo molecular pump side. A rate of change of the lead angle ϕalso becomes smaller as approaching to the exhaust port side from the turbo molecular pump side. As a result, a rate of a part wherein the lead angle ϕis small is increased and the compression performance is improved. Thus, an auxiliary pump exhibiting a lower exhaust speed than a conventional one can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular pump having a drag pump mechanism and a vacuum pumping apparatus equipped with the molecular pump.

[0002]

2. Description of the Related Art Conventionally, since a semiconductor manufacturing apparatus such as an etching apparatus or a CVD apparatus performs each process while flowing a process gas, a large flow type composite turbo-molecular pump is used. The hybrid turbo molecular pump is
It is composed of a turbo molecular pump section having a turbine blade and a drag pump section having a thread groove. The turbo molecular pump unit cannot compress the gas taken in from the intake port to atmospheric pressure, so normally an auxiliary pump is connected to the exhaust port side of the turbo molecular pump unit and the exhausted gas is compressed to atmospheric pressure by the auxiliary pump. I am trying to do it.

When a turbo molecular pump is used in a semiconductor manufacturing apparatus, a dry vacuum pump is generally used as an auxiliary pump due to the requirement of being oil-free. Since the dry vacuum pump consumes a large amount of power, it is desired to use a small dry vacuum pump that consumes less power from the viewpoint of energy saving.

[0004]

However, when a small dry vacuum pump having a small exhaust speed is used, the exhaust port pressure of the turbo molecular pump tends to increase when the process gas is supplied. Therefore, the conventional turbo molecular pump has a problem that the compression capacity is insufficient and the pressure on the intake port side of the turbo molecular pump, that is, the pressure in the vacuum chamber rises, and the desired process pressure cannot be obtained.

An object of the present invention is to provide a molecular pump having excellent compression performance, and a vacuum exhaust device equipped with the molecular pump.

[0006]

An embodiment of the invention will be described with reference to FIGS. 1, 2, 5 and 10. (1) Explaining in association with FIGS. 1, 2 and 5, the invention of claim 1 is a drag pump portion M having a thread groove 51.
The lead angle φ of the thread groove 51 is reduced as approaching from the intake side to the exhaust side.
In addition, the above-described object is achieved by reducing the rate of change d ² y / dx ² of the lead angle φ as it approaches the exhaust side from the intake side. (2) The invention of claim 2 is applied to the molecular pump 1 provided with the drag pump portion M having the thread groove 51, and is a curve CD which is a part of the curve y = −b · x ^0.5 on the xy coordinate plane. Is the lead shape of the screw groove 51, the end C on the coordinate origin side of the partial curve CD is the intake side of the screw groove 51, and the other end D of the partial curve CD is the screw groove 5
The above-described object is achieved by adopting the exhaust side of 1. However, b is an arbitrary positive real number. (3) Describing in association with FIG. 10, the vacuum exhaust device according to the invention of claim 3 is the molecular pump 1 according to claim 1 or 2, and an auxiliary pump 68 connected to the exhaust port 3 of the molecular pump 1. The above object is achieved by providing

In the section of the means for solving the above problems, the drawings of the embodiments of the present invention are used to make the present invention easy to understand, but the present invention is limited to the embodiments of the present invention. Not something.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a hybrid turbomolecular pump according to the present invention. A chamber (not shown) to be evacuated is connected to the intake port flange 2a of the turbo molecular pump 1. On the other hand, an auxiliary pump (not shown) such as a dry pump is connected to the exhaust port flange 3. Inside the outer cylinder 2 having the intake port flange 2a formed therein, a rotary cylindrical portion 4b having a plurality of stages of rotary blades 4a and screw grooves 51 formed therein.
A rotor 4 having a and is rotatably arranged. Fixed blades 5a are arranged between the rotating blades 4a arranged vertically, and a fixed cylindrical portion 5b is arranged so as to surround the periphery of the rotating cylindrical portion 4b. As will be described later, a thread groove 51 is formed on the inner peripheral surface of the fixed cylindrical portion 5b.

In the hybrid turbo molecular pump 1, the rotary blade 4
a and the fixed blade 4b constitute a turbo molecular pump unit T, and the rotary cylindrical unit 4b and the fixed cylindrical unit 5b form a drag pump unit M.
Are configured. The composite turbomolecular pump 1 shown in FIG. 1 is a magnetic bearing type turbomolecular pump, and the rotor 4 is a radial electromagnet 6A, 6B and an axial electromagnet 6C.
Is supported in a non-contact manner by the high frequency motor 7 and is rotationally driven by the high frequency motor 7. The rotor 4 is supported by an emergency mechanical bearing 8 when it is not magnetically levitated. During magnetic levitation, the rotor 4 and the mechanical bearing 8 are in a non-contact state.

When the rotor 4 is driven to rotate at a high speed by the high-frequency motor 7, the gas molecules that have jumped from the intake flange 2a to the turbo molecular pump 1 side have a turbo molecular pump section T.
And is discharged to the drag pump section M side. In the drag pump section M, the gas compressed by the turbo molecular pump section T is further compressed and exhausted to the exhaust port flange 3 side. The gas exhausted to the exhaust port flange 3 side is exhausted to the atmospheric pressure side by the dry pump connected to the exhaust port flange 3.

FIG. 2 is a development view showing the screw groove 51 formed on the inner peripheral surface of the fixed cylindrical portion 5b. In FIG. 2, the X-axis represents the length of the thread groove surface in the developing direction (circumferential direction), the upper side in the figure (the positive side of the y-axis) is the turbo molecular pump section side, and the lower side in the figure is the exhaust port side. is there. In addition, the angle (0 to 360 °) when developed is also referred to. Fixed cylindrical part 5b
A plurality of screw grooves 51 are formed on the inner peripheral surface of the, and convex portions 52 are formed between the screw grooves. FIG. 3 is a view showing a cross section taken along the line AA in FIG. 2, and 51 a is a boundary between the screw groove 51 and the convex portion 52. φ is the inclination angle of the boundary 51 a and represents the lead angle of the thread groove 51. The lead angle on the turbo molecular pump side is φ1, and the lead angle on the exhaust port side is φ2.
1> φ2. The depth of the screw groove 51 becomes shallower toward the exhaust port side.

<< Lead Angle of Conventional Thread Groove >> The exhaust performance of the drag pump M is as follows: the lead angle φ of the thread groove 51, the width of the thread groove 51, the depth of the thread groove 51, the rotating cylindrical portion 4b and the fixed cylindrical portion. It depends on the size of the gap with 5b. As for the lead angle φ, as the angle becomes smaller, the compression performance of the drag pump portion M improves. In the molecular pump, the ratio of the pressure on the exhaust port side to the pressure on the intake port side (turbo molecular pump side) is called the compression ratio, and the compression performance is judged by this compression ratio. Conventionally, the lead angle φ was initially constant because of the ease of processing the thread groove.

After that, the lead angle φ on the intake side is made relatively large to facilitate the acceptance of gas molecules, and the lead angle φ on the exhaust port side is made small to remove gas molecules flowing back from the exhaust port side to the drag pump section side. What was suppressed was invented. At this time, the lead shape of the thread groove corresponding to the shape of the boundary 51a in FIG. 3 is y in the axial direction of the fixed cylindrical portion in the development view and x in the development direction.
Then, it is represented by the equation (1).

[Formula 1] y = a · x ² (1)

FIG. 4A shows a curve y = a · x ² , which is a curve on the curve y = a · x ² from a point A with an inclination angle of φ1 to a point B with an inclination angle of φ2. AB had a thread groove shape. At this time, the lead angle φ of the screw groove gradually decreases from φ1 on the turbo molecular pump portion side (point A), and becomes φ2 on the exhaust port side (point B). By the way, regarding the lead angle φ, the first-order derivative dy / dx of the curve y = a · x ² represents the slope tan φ of the curve (FIG. 4 (b)). Also, FIG.
The second derivative d ² y / dx ² shown in (c) is the rate of change of the slope tan φ. That is, since the rate of change of the slope tanφ of the curve AB is constant at 2a, the rate of change of the lead angle φ is also constant. As described above, the conventional thread groove represented by the formula (1) has a constant rate of change of the lead angle φ (= 2).
a).

<< Screw Groove Shape in the Present Embodiment >> FIG.
FIG. 4 is a diagram showing an example of a thread groove shape in the present embodiment. FIG. 5A illustrates the curve y ² = b ² · x, and the lower half thereof is represented as y = −b · x ^0.5 .
Then, the shape (lead shape) of the boundary 51a of the thread groove 51 described above is made to be the same shape as the curve CD from the point C (lead angle φ1) to the point D (lead angle φ2). FIG. 5B shows a curve y = −b · x ^0.5 first derivative dy / d.
5C shows the second derivative d ² y / dx ² of the curve y = −b · x ^0.5 .

As can be seen from FIG. 5 (c), the curve CD
In, the rate of change of the slope tanφ of the curve decreases as it approaches x (C) from x (C). That is, it can be seen that, in the case of the curve CD, the proportion of the portion having the inclination close to the lead angle φ2 is larger than that of the curve AB in which the rate of change of the curve tan φ is constant. The shapes of the boundaries 51a shown in FIG. 2 are all the same, and they are obtained by translating the curve CD in the x-axis direction of FIG.

FIG. 6 shows a lead shape of the thread groove 51 (curve indicated by a white circle) in the present embodiment and a lead shape based on a curve AB in which the rate of change of the lead angle is constant as in the conventional case (curve indicated by a black circle). ) And is shown. In FIG. 6, the vertical axis represents the axial dimension of the fixed cylindrical portion 5b.
And the horizontal axis corresponds to the x-axis, which is the dimension in the expansion direction when the thread groove surface is expanded. In addition, in order to make it easier to understand the difference in lead shape, in FIG.
The point A and the point C in FIG. The lead angles at points A and C are set to φ1 = 26 °, and the lead angles at points B and D are set to φ2 = 14 °.

As shown in FIG. 6, the axial dimension of the thread groove is 1
If it is set to 60 (mm), the lead shape in the case of the present embodiment becomes b = 12.8 in the curve y = −b · x ^0.5 , and the x coordinate of the point C in FIG. Is x (C) = 1
At 70 (mm), the x coordinate of the point D is x (D) = 656 (m
m). On the other hand, (a curve shown by black circles) constant changes lead angle of the lead shape, the curve y = a · x ² a =
2.75 × 10 ⁻³ , the x coordinate of point A in FIG. 4A is x (A) = − 887 (mm), and the x coordinate of point B is x (B) = − 452. (Mm). In FIG. 6, point A,
Since the x-coordinate of C is 0, the x-coordinates of points B and D in FIG. 6 are x (B) = 435 (mm) and x, respectively.
(D) = 486 (mm).

For example, φ = 1 for each lead shape
When the range of 4 ° to 16 ° is shown, R1 and R of FIG.
It becomes the range shown by 2. The range R1 in the conventional case is about 16% with respect to the entire lead shape, while the range R2 in the present embodiment is about 33%. As a result, the compression performance is improved over the conventional case. Further, since the lead angle on the turbo molecular pump side is set to φ1 = 26 ° as in the conventional case, there is almost no difference in acceptability of gas molecules (exhaust velocity performance).

In the above-described embodiment, the lead shape is a part of the curve y = -b · x ^0.5 , but the present invention is not limited to this.
As shown in FIG. 5C, the curve may be such that the rate of change of the lead angle φ decreases from the intake port side (point C) toward the exhaust port side (point D). For example, it may be a part (curve EF) of the curve y = k · x ⁴ as shown in FIG. 7. In FIG. 7, (a) is a diagram showing a curve y = k · x ⁴ , (b) shows a first derivative dy / dx, and (c) shows a second derivative d ² y / dx ² . Also in this case, as the point E approaches the point F, the second derivative d ² y / dx ^2, which is the rate of change of the lead angle φ, decreases.

FIG. 8 shows the exhaust performance of the conventional composite turbo molecular pump having the lead shape of the curve AB and the exhaust performance of the composite turbo molecular pump of the present embodiment having the lead shape of the curve CD. FIG. In FIG.
The relationship between the inlet pressure and the outlet pressure of the turbo molecular pump when a certain amount of nitrogen gas flows into the exhaust chamber is shown. The turbo molecular pump illustrated in FIG.
2000 (L / s used for dry etching equipment, etc.
ec) It is a class pump. L10 and L11 relate to the turbo molecular pump of the present embodiment, and L2
0 and L21 relate to a conventional turbo molecular pump. Also,
L10 and L20 are nitrogen gas 1000 (SCCM)
When inflowing, L11 and L21 are nitrogen gas 500
(SCCM) when inflow.

In the case of the turbo molecular pump of this embodiment,
Since the compression performance is improved as compared with the conventional turbo molecular pump as described above, even if the exhaust port pressure is increased to about 1200 (Pa), the intake port pressure (that is, the chamber internal pressure) is kept constant. You can On the other hand, in the case of the conventional turbo molecular pump, the exhaust port pressure is 300 (P
When it rises to about a), the inlet pressure starts to rise.
Therefore, it is understood that stable exhaust cannot be performed unless the exhaust port pressure is made lower than 300 (Pa) using a larger auxiliary pump.

For example, when an auxiliary pump having an exhaust speed of 300 (L / min) is shown in FIG. 8, it becomes P0 and P1.
P0 indicates the intake port pressure of the auxiliary pump when 1000 (SCCM) nitrogen gas is exhausted by this auxiliary pump, that is, the exhaust port pressure of the turbo molecular pump. Also,
P1 represents the inlet pressure of the auxiliary pump when 500 (SCCM) nitrogen gas is exhausted by this auxiliary pump. P0 indicates that the inlet pressure of the auxiliary pump is about 400 (Pa) when the flow rate is 1000 (SCCM), while P1 indicates that the inlet pressure of the auxiliary pump is about 200 (Pa) when the flow rate is 500 (SCCM). It shows that it becomes. That is, in the turbo molecular pump of the present embodiment, even if the gas flow rate is 1000 (SCCM),
An auxiliary pump of the (L / min) class can be used.

On the other hand, in the case of the conventional turbo molecular pump, if the flow rate is 500 (SCCM), the auxiliary pump intake port pressure is about 200 (Pa) as indicated by P1, so 300
An auxiliary pump of the (L / min) class can be used. However, the auxiliary pump intake port pressure when the flow rate is 1000 (SCCM) is 400 (Pa) as indicated by P0.
However, the intake pressure of the turbo molecular pump rises and stable exhaust cannot be performed. That is, flow rate 1
When used at 000 (SCCM), it is necessary to lower the exhaust port pressure of the turbo molecular pump below 200 (Pa) by using an auxiliary pump having a higher pumping speed.

9 and 1 show examples of pump arrangements when a vacuum evacuation device that combines such a turbo molecular pump and a dry vacuum pump is used in a dry etching device.
It shows in 0. FIG. 9 is a diagram when the conventional turbo molecular pump 64 is used, and the auxiliary pump 1000 to 3000 is used.
(L / min) dry vacuum pump 66 is used.
Semiconductor manufacturing factories generally have a two-layer structure, with a clean room on the second floor and a machine room on the first floor. The etching apparatus 60 includes a process chamber 61 and a transfer chamber 6
2. The process chamber 61 has a load lock chamber 63.
A turbo molecular pump 64 is connected to the valve via a valve 69.

Conventionally, the dry vacuum pump 66, which is an auxiliary pump of the turbo molecular pump 64, has a large volume and a large weight, and therefore is separated from the etching apparatus 60 and disposed in the machine room on the first floor. The exhaust port of the turbo molecular pump 64 and the intake port of the dry vacuum pump 65 are connected by a pipe 65. Since the dry vacuum pump 66 is arranged in the machine room, there is a limit to the shortening of the pipe 65, and in order to reduce the pipe resistance to the gas flow, the pipe 65 having the largest inner diameter is used.

On the other hand, FIG. 10 is a diagram showing the arrangement when the turbo-molecular pump 1 of the present embodiment is used. As described above, the turbo molecular pump 1 has a higher compression performance than the conventional turbo molecular pump 64.
~ 500 (L / min) small dry vacuum pump 68
Can be used. As a result, not only the turbo molecular pump 1 but also the dry vacuum pump 68 is etched.
It becomes possible to incorporate in 0. Therefore, the length of the pipe 70 connecting the exhaust port of the turbo molecular pump 1 and the intake port of the dry vacuum pump 68 can be shortened, and the pipe diameter may be smaller than that in the conventional case (FIG. 9). further,
The dry vacuum pump 66, which used to be in the 1000 to 3000 (L / min) class, is now 100 to 500 (L / min).
Since the n-class small dry vacuum pump 68 can be replaced, the total power consumption of the etching apparatus 60 can be significantly reduced.

In the above-described embodiment, the hybrid turbo molecular pump including the turbo molecular pump section T and the drag pump section M has been described as an example, but the present invention is applicable to a molecular pump including only the drag pump section. Can also be applied. Further, although the thread groove is formed on the surface (inner peripheral surface) of the fixed cylindrical portion 5b facing the rotating cylindrical portion 4b, the thread groove 51 may be formed on the rotating cylindrical portion 4b side. Furthermore, the screw groove 51 does not have to be formed in the entire area of the drag pump portion M in the vertical direction, and may be formed in a part thereof.

Further, as shown in FIG. 11A, the fixed cylindrical portion 5c having the thread groove 51 may be arranged inside the rotating cylindrical portion 4b of the rotor 4. Further, FIG. 11 (b)
As shown in FIG. 5, the fixed cylindrical portion 5d having the thread groove 51 is formed.
May be provided on both inner and outer sides of the rotating cylindrical portion 4b.

In the correspondence between the embodiment described above and the elements of the claims, the curve CD is a part of claim 2, the point C is the end on the coordinate origin side, and the point D is the other end. ,
The exhaust port flange constitutes the exhaust port of claim 3, respectively.

[0031]

As described above, according to the present invention,
Since the rate of change of the lead angle of the thread groove is made smaller as it approaches from the intake side to the exhaust side, the proportion of the portion having a small lead angle on the exhaust port side is larger than in the conventional case, and the compression performance of the pump is improved. As a result, it becomes possible to use a small auxiliary pump having a low pumping speed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a hybrid turbo molecular pump.

FIG. 2 is a thread groove 5 formed on an inner peripheral surface of a fixed cylindrical portion 5b.
It is a development view showing 1.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a diagram illustrating a conventional lead shape, (a)
Shows a curve y = a · x ² , (b) shows a curve y = a · x
² is a diagram showing the first derivative dy / dx of FIG. 2, (c) is a curve y = a
- is a diagram showing the second derivative ^{d 2} y / dx 2 of ^{x 2.}

FIG. 5 is a diagram for explaining a lead shape in the present embodiment, (a) is a diagram showing a curve y = −b · x ^0.5 ,
(B) is a curve y = −b · x ^0.5 first-order derivative dy / dx
FIG. 3C is a diagram showing a second derivative d ² y / dx ² of the curve y = −b · x ^0.5 .

FIG. 6 is a view showing a lead shape in the present embodiment and a conventional lead shape under the same conditions.

FIG. 7 is a diagram illustrating another example of the lead shape,
(A) is a diagram showing a curve y = k · x ⁴ , and (b) is a curve y =
shows the first derivative dy / dx of k · ^{x 4,} a diagram illustrating the second derivative ^{d 2} y / dx 2 (c), the curve y = k · ^{x 4.}

FIG. 8 is a diagram showing the exhaust performance of the composite turbo-molecular pump of the present embodiment in comparison with the conventional one.

FIG. 9 is a diagram showing a conventional vacuum exhaust device.

FIG. 10 is a diagram showing an evacuation device according to the present invention.

FIG. 11 is a view showing a modified example of the drag pump unit,
(A) is a figure showing the 1st modification, and (b) is a figure showing the 2nd modification.

[Explanation of symbols]

1,64 Hybrid turbo molecular pump 2 outer cylinder 3 Exhaust port flange 4 rotor 4a rotor 4b rotating cylinder 5a fixed wing 5b Fixed cylindrical part 51 screw groove 51a border 52 convex 60 etching equipment 66,68 Dry pump M Drag pump section T turbo molecular pump section φ, φ1, φ2 lead angle

Claims (3)

[Claims] 1. A molecular pump comprising a drag pump section having a thread groove, wherein the lead angle of the thread groove is reduced as it approaches the exhaust side from the intake side, and the rate of change of the lead angle is changed from the intake side. A molecular pump characterized by being made smaller as it approaches the exhaust side. 2. A molecular pump provided with a drag pump unit having a thread groove, wherein a part of a curve y = −b · x ^0.5 on an xy coordinate plane has a lead shape of the thread groove, and A molecular pump, wherein an end on a coordinate origin side is an intake side of the thread groove, and another end of the part is an exhaust side of the thread groove. However, b is an arbitrary positive real number. 3. A vacuum exhaust device comprising the molecular pump according to claim 1 or 2, and an auxiliary pump connected to an exhaust port of the molecular pump.